Semiconductor device encapsulated with an epoxy resin and a process for encapsulation

ABSTRACT

A process for encapsulating a semiconductor device involves the step(s) of encapsulating the device with an epoxy resin composites represented by the formula (2) ##STR1## in which R 1  to R 4  independently represent hydrogen, an alkyl or cycloalkyl group having 1 to 9 carbon atoms, or halogen, and X represents hydrogen, an alkyl group having 1 to 9 carbon atoms, or an aryl and n represents an average number of repeating units of 0.1 to 1.6; and a curing agent.

This is a division of application Ser. No. 08/328,771, filed Oct. 27,1994, now U.S. Pat. No. 5,462,997, which is a divisional of Ser. No.08/155,181, filed Nov. 22, 1993 and now U.S. Pat. No. 5,395,912, whichis a continuation of Ser. No. 07/957,875, filed Oct. 8, 1992, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel polyhydric phenol and an epoxyresin and an epoxy resin composition useful for encapsulating electronicdevices derived from the polyhydric phenol as starting material.

2. Description of the Related Art

Recently, semiconductors such as LSI, IC, transistors and the like havebeen encapsulated by transfer molding with epoxy resins which areeconomically advantageous. Particularly, many of practical package havebeen recently mounted by surface mounting technology, so that immersionof them directly into a solder bath has been increasingly performed.During the immersion, the encapsulating materials are exposed to hightemperatures of 200° C. or more to cause expansion of the moisture whichhas been hygroscopically sorbed in the encapsulating materials.Therefore, the encapsulating materials become more prone to cracking.

For this reason, the epoxy encapsulating materials are required to havea resistance to cracking, especially much less hygroscopicity than theordinary level thereof. Currently the most popular encapsulatingmaterials are those using a glycidyl ether of o-cresol novolak, andpackaged practically in moisture-proof wraps to be marketed and storedwith moisture absorption being inhibited.

The encapsulating materials comprising a major component of glycidylether of o-cresol novolak are not only excellent in heat resistance, butalso good to some extent in balance of heat resistance and lesshygroscopicity. However, they are not necessarily satisfactory in suchapplications as a greater degree of less hygroscopicity being requiredas described above. Therefore, there has been desired an improvement ofthe encapsulating materials.

In addition, for example, cured products from difunctional epoxy resinssuch as glycidyl ether of bisphenol cyclohexane have an inferior thermalresistance as well as an insufficient curing property though they areexcellent in less hygroscopicity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an epoxy resincapable of producing a cured product which is excellent in lesshygroscopicity and has a balance between the thermal resistance and thecuring property, and a polyhydric phenol as starting material for theepoxy resin.

The present invention can be described as follows:

1. A polyhydric phenol represented by the general formula (1): ##STR2##wherein R₁ to R₄ independently represent hydrogen, an alkyl orcycloalkyl group having 1 to 9 carbon atoms, or halogen, and Xrepresents hydrogen, an alkyl group having 1 to 9 carbon atoms, or anaryl group, and n represents an average number of repeating units of 0.1to 10.

2. An epoxy resin represented by the general formula (2): ##STR3##wherein R₁ to R₄ independently represent hydrogen, an alkyl orcycloalkyl group having 1 to 9 carbon atoms, or halogen, and Xrepresents hydrogen, an alkyl group having 1 to 9 carbon atoms, or anaryl, and n represents an average number of repeating units of 0.1 to10.

3. An epoxy resin composition comprising said epoxy resin and a curingagent.

4. A process for using the epoxy resin composition for encapsulating asemiconductor device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The substituents R₁ to R₄ contained in the polyhydric phenol representedby the general formula (1) and the epoxy resin represented by thegeneral formula (2) according to the present invention include hydrogen,methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl,nonyl, chlorine, and bromine, including various isomers.

The substituent X includes hydrogen, methyl, ethyl, propyl, butyl, amyl,hexyl, cyclohexyl, heptyl, octyl, nonyl, phenyl, and naphtyl, includingvarious isomers thereof.

The average number of repeating units, n, is 0.1 to 10, preferably 0.1to 5, more preferably 0.1 to 2. The n higher than 10 results undesirablyin poor workability with an increase in viscosity.

Polyhydric phenols according to the present invention can be produced bycondensation of a bisphenol represented by the general formula (3):##STR4## wherein R₁ to R₄ are the same as those defined for the generalformula (1), and an aldehyde represented by the general formula (4):##STR5## wherein X is the same as that defined for the general formula(1), in the presence of an acidic catalyst.

The polyhydric phenol according to the present invention may be producedby one of known methods comprising condensing an aldehyde as describedabove with a bisphenol as described above in the presence of an acidiccatalyst such as an inorganic acid such as hydrogen chloride andsulfuric acid, an organic acid such as acetic acid, p-toluene sulfonicacid, thioglycollic acid, or a Lewis acid.

The polyhydric phenol according to the present invention is a novelcompound, and expected to be useful for applications such as synthesisof epoxy resins and various phenol resins.

Bisphenols used in the present invention may be produced by any one ofknown methods comprising condensing a cyclohexanone as defined belowwith a phenol as defined below in a molar ratio of two times or more themolar amount of the cyclohexanone in the presence of an acidic catalystsuch as an inorganic acid such as hydrogen chloride and sulfonic acid,an organic acid such as acetic acid, p-toluene sulfonic acid,thioglycollic acid, or a Lewis acid, washing with water, distilling outunreacted phenols, and if necessary, conducting post-treatment such asrecrystallization from poor solvent. In the process, phenols may be leftin the bisphenols to such an extent as not diminishing the effects ofthe present invention.

Exemplary phenols include phenol, cresol, ethyl phenol, propyl phenol,butyl phenol, amyl phenol, hexyl phenol, cyclohexyl phenol, octylphenol, nonyl phenol, xylenol, methylbutyl phenol, chlorophenol,bromophenol, dichlorophenol, and dibromophenol, including variousisomers thereof. These phenols may be used as alone as well as in amixture of two or more thereof.

Exemplary cyclohexanones include cyclohexanone, mono-, or di-alkylcyclohexanone and the like. The alkyl group includes those having 1 to 9carbon atoms.

Exemplary aldehydes represented by the general formula (4) to be used inthe present invention include formaldehyde, acetaldehyde, butylaldehyde,benzaldehyde, naphthaldehyde, and the like.

Moreover, the said polyhydric phenols may be substituted with halogenssuch as chlorine and bromine for imparting flame retardance.

The epoxy resin according to the present invention can be produced byglycidyl-etherifying the polyhydric phenol obtained in the procedure asdescribed above, i.e., by a known method comprising reacting thepolyhydric phenol with an epihalohydrin in the presence of an alkalisuch as caustic soda. Particularly, if desired to produce a highly pureproduct, a reaction in an aprotic solvent is preferred as disclosed inJapanese Patent KOKAI (Laid-open) No. Sho 60-31517.

From the epoxy resin according to the present invention, there canproduce a cured product by using an ordinary epoxy curing agent.

Exemplary curing agents include polyhydric phenols such as phenolnovolak, amine based curing agents such as dicyandiamide,diaminodiphenylmethane, diaminodiphenylsulfonic acid, acid anhydridebased curing agents such as pyromellitic acid anhydride, trimelliticacid anhydride, benzophenonetetracarboxylic acid anhydride, withpolyhydric phenols being preferred.

Exemplary polyhydric phenols as curing agents include polycondensates ofone or more kinds of phenols such as phenol, alkylphenol, naphtol, orthe like with an aldehyde such as formaldehyde, acetaldehyde, acrolein,glyoxal, benzaldehyde, naphtaldehyde, hydroxybenzaldehyde, or the likeand/or a ketone such as cyclohexanone, acetophenone, or the like;vinylpolymer type polyhydric phenols such as polyvinylphenol andpolyisopropenylphenol; Friedel-Crafts reaction products of a phenol witha diol such as a diol represented by the general formula: ##STR6## orwith a dialkoxide such as a dialkoxide represented by the generalformula: ##STR7## or with a dihalide such as a dihalide represented bythe general formula: ##STR8## or with a diolefin such asdicyclopentadiene, diisopropenylbenzene or the like.

The amount of these curing agents to be used is 0.7 to 1.2 equivalentsbased on the epoxy group. An amount of the curing agents of lower than0.7 equivalent or over 1.2 equivalents based on the epoxy group resultin insufficient cure.

Furthermore, to the composition there may be added known additives suchas fillers, curing accelerators, flame retardants, mold releasingagents, surface treating agents and the like depending upon the end use.

The fillers include silica, alumina, aluminum hydroxide, talc, clay andglass fibers. These may be used in a mixture of different shapes (sphereor crashed types) and different sizes to increase the filler volume. Thecuring accelerators include imidazoles, tertiary amines, phosphoruscompounds, and the like. The flame retardants include brominated epoxyresins, antimony trioxide, and the like.

The mold releasing agents include waxes, metal salts of higher fattyacids such as zinc stearate, and the surface treating agents includesilane coupling agents and the like.

In order to reduce stresses imposed, various elastomers may be added orpre-reacted. Practically, one may make mention of additive or reactivetype elastomers such as polybutadiene, butadiene-acrylonitrilecopolymer, silicone rubbers, and the like.

With the resin composition of the present invention, electronic parts ofsemiconductors and the like can be encapsulated by molding and curingaccording to any one of known prior techniques such as transfer molding,compression molding, injection molding and the like.

Cured products from the epoxy resins of the present invention have alower hygroscopic property compared to the conventional products and abalance between the thermal resistance and the curing property so thatthey are highly suitable for practical use particularly as encapsulatingmaterials for electronic devices. The polyhydric phenols according tothe present invention are important as starting material for epoxyresins.

The present invention will be illustrated with reference to thefollowing Examples, without being limited thereto. In Examples, epoxyequivalent weight is defined as a molecular weight of an epoxy resin perepoxy group. Hydrolyzable chlorine content was determined by dissolvingan epoxy resin into dioxane, adding a solution of potassium hydroxide inalcohol, heating the solution at reflux for 30 minutes to releasechloride ions, the amount of which was back titrated with an aqueoussolution of silver nitrate to be expressed in terms of parts per millionof said epoxy resin. The average number of repeating units wasdetermined with GPC (TRIROTOR SR-II, available from NIPPON BUNKO KOGYO,Ltd.

Cured materials were evaluated as follows:

Glass transition temperature: Determination was effected using athermomechanical analyzer (SHIMADZU DT-30).

Barcol hardness: Determination was made with a hard tester model 935according to ASTM D-648.

Flexural strength, flexural modulus: Determination was made with anInstron universal tester (SHIMADZU IS-10T) according to JIS K-6911.

Water absorbance: A variation in weight was measured at a temperature of85° C. and a relative humidity of 85% using a thermostat (TABAI PR-2)under a constant humidity.

Spiral flow: Conducted at a temperature of 175° C. and at 70 kg/cm².

REFERENTIAL EXAMPLE

147.3 g of cyclohexanone were added to a reactor equipped with athermometer, a stirrer, and a condenser, dissolved into 648.6 g ofo-cresol, added with 600 g of concentrated hydrochloric acid, andstirred at 60° C. for 10 hours.

After the reaction was completed, toluene was added to produce aprecipitate containing a condensate of o-cresol with cyclohexanone, andthe precipitate was separated by filtration. The obtained precipitatewas washed with water to remove hydrochloric acid, thereby givingbis-o-cresol cyclohexane.

FD-MASS spectroscopy indicated that the product had a molecular weightof 296 and a melting point of 190 to 195° C.

1. Synthesis of polyhydric phenols

EXAMPLE 1

To a reactor equipped with a thermometer, a stirrer, and a condenser,100 g of bis-o-cresolcyclohexane, 1.92 g of p-toluene sulfonic acidmonohydrate and 150 g of methylisobutylketone were added, and afterdissolved, 8.15 g of a 37% formalin were continuously added dropwise ata temperature of 80° C. for 2 hours, and then the whole was kept at atemperature of 80° C. for 2 hours as it was. After neutralizing withcaustic soda, washing with water, and concentrating under reducedpressure, bis-o-cresolcyclohexane novolak was obtained.

By FD-MASS spectroscopy, fragments of 296, 604, 912, and 1220 weredetected. The average number of repeating units, n, determined by GPCwas 0.68.

EXAMPLE 2

To a reactor equipped with a thermometer, a stirrer, and a condenser,100 g of bisphenolcyclohexane (available from SUMITOMO Chemical Co.,Ltd, under the trade name of Antigen W), 1.92 g of p-toluene sulfonicacid monohydrate and 150 g of methylisobutylketone were added, and afterdissolved, 8.15 g of a 37% formalin were continuously added dropwise ata temperature of 80° C. for 2 hours, and then the whole was kept at atemperature of 80° C. for 2 hours as it was. After neutralizing withcaustic soda, washing with water, and concentrating under reducedpressure, bisphenolcyclohexane novolak was obtained.

By FD-MASS spectroscopy, fragments of 268, 548, and 828 were detected.The average number of repeating units, n, determined by GPC was 0.53.

EXAMPLE 3

To a reactor equipped with a thermometer, a stirrer, and a condenserhaving a water separator, 160.8 g of bisphenolcyclohexane, 3.42 g ofp-toluene sulfonic acid monohydrate, 160.8 g of isoamylalcohol and 19.1g of benzaldehyde were added. After dissolved, the solution wasdistilled under reduced pressure of 70 torr at a temperature of 80° C.to distill out isoamylalcohol and water which were cooled into liquid.While returning the organic layer into the reactor, the reaction wasconducted for 4 hours. After neutralizing with caustic soda, washingwith water, and concentrating under reduced pressure,bisphenolcyclohexane benzaldehyde condensate was obtained.

By FD-MASS spectroscopy, fragments of 268, 624, 980, and 1336 weredetected. The average number of repeating units, n, determined by GPCwas 1.56.

EXAMPLE 4

Using 100 g of bisphenolcyclohexane, 2.31 g of p-toluene sulfonic acidmonohydrate, 150 g isoamylalcohol and 17.5 g of naphthaldehyde,bisphenolcyclohexane naphthaldehyde condensate was obtained in the samemanner as in Example 3.

By FD-MASS spectroscopy, fragments of 268, 674, and 1080 were detected.The average number of repeating units, n, determined by GPC was 0.67.

2. Synthesis of epoxy resins

EXAMPLE 5

To a reactor equipped with a thermometer, a stirrer, and a condenserhaving a water separator, 150 g of bis-o-cresolcyclohexane novolakobtained in Example 1 were added, and dissolved in 647.6 g ofepichlorohydrin and 323.8 g of dimethyl sulfoxide. The solution wasadded with 8.8 g of a 48.6% caustic soda while maintaining thetemperature at 40° C. and further warmed at that temperature for 6hours. To the reaction phase kept under a pressure of 41 torr, 69.4 g ofa 48.6% caustic soda were continuously added dropwise at a temperatureof 48° C. for 4 hours. During the addition, the temperature was kept at48° C. with azeotropically distilled epichlorohydrin and water beingcooled to liquid. While returning the organic layer into the reactor,the reaction was conducted for 4 hours.

After the reaction was completed, unreacted epichlorohydrin was removedout by concentration under reduced pressure, and a glycidyl ethercontaining by-product salt and dimethyl sulfoxide was dissolved intomethylisobutylketone and washed with water to remove out the by-productsalt and dimethyl sulfoxide.

The thus obtained glycidyl ether had an epoxy equivalent weight of 227g/eq. and a hydrolyzable chlorine content of 280 ppm.

EXAMPLE 6

A glycidyl ether was produced in the same manner as in Example 5, exceptthat 136 g of bisphenolcyclohexane novolak obtained in Example 2 wereused. The produced glycidyl ether had an epoxy equivalent weight of 208g and a hydrolyzable chlorine content of 200 ppm.

EXAMPLE 7

A glycidyl ether was produced in the same manner as in Example 5, exceptthat 136 g of bisphenolcyclhexane benzaldehyde condensate obtained inExample 3 were used. The produced glycidyl ether had an epoxy equivalentweight of 226 g/eq. and a hydrolyzable chlorine content of 220 ppm.

EXAMPLE 8

A glycidyl ether was produced in the same manner as in Example 5, exceptthat 136 g of bisphenolcyclhexane naphthaldehyde condensate obtained inExample 4 were used. The produced glycidyl ether had an epoxy equivalentweight of 228 g/eq. and a hydrolyzable chlorine content of 260 ppm.

COMPARATIVE EXAMPLE 1

500 g of 2,6-xylenol were treated in the identical procedure to thatdisclosed in Example 1 of Japanese Patent KOKAI (Laid-open) No. Hei1-283241 to produce 3,3',5,5'-tetramethylbiphenol.

A glycidyl ether was produced in the same manner as in Example 5, exceptthat 121 g of 3,3',5,5'-tetramethylbiphenol were used. The producedglycidyl ether had an epoxy equivalent weight of 194 g/eq. and ahydrolyzable chlorine content of 220 ppm.

COMPARATIVE EXAMPLE 2

A glycidyl ether was produced in the same manner as in Example 5, exceptthat 134 g of bisphenolcyclhexane were used. The produced glycidyl etherhad an epoxy equivalent weight of 201 g/eq. and a hydrolyzable chlorinecontent of 330 ppm.

3. Evaluation of the composition and the cured materials

EXAMPLES 9 TO 12 AND COMPARATIVE EXAMPLES 3 TO 5

The epoxy resins obtained in the above Examples, a phenol novolak ascuring agent (available from ARAKAWA Chemical Industry Co. Ltd. underthe trade name of TAMANOL 759), triphenyl phosphine as curingaccelerator, fused silica as filler (available from Electric ChemicalIndustry Co. Ltd. under the trade name of FS-891), carnauba wax as moldreleasing agent, a coupling agent (available from TORE DOW CORNINGSILICONE under the trade name of SH-6040) were incorporated in amounts(g) as indicated in Table 1, heat-kneaded with a roll, and transfermolded. Then, the moldings were post-cured for 5 hours in an oven at atemperature of 180° C. to produce cured materials.

The compositions were measured for spiral flow and the cured materialsfor glass transition temperature, water absorbance (a measure ofhygroscopicity), flexural strength, flexural modulus. The results areset forth in Table 2.

                                      TABLE 1                                     __________________________________________________________________________                              Comp.                                                                              Comp.                                                                              Comp.                                     Ex. 9      Ex. 10                                                                             Ex. 11                                                                             Ex. 12                                                                             Ex. 3                                                                              Ex. 4                                                                              Ex. 5                                     __________________________________________________________________________    Glycidyl                                                                            Ex. 5                                                                              Ex. 6                                                                              Ex. 7                                                                              Ex. 8                                                                              Note 1                                                                             Comp.                                                                              Comp.                                     ether                          Ex. 1                                                                              Ex. 2                                     Amount                                                                              100  100  100  100  100  100  100                                       Phenol                                                                              48.5 52.9 48.9 48.2 56.0 56.7 54.7                                      novolak                                                                       Triphenyl                                                                           1.5  1.5  1.5  1.5  1.5  1.5  1.5                                       phosphine                                                                     Filler                                                                              347  357  347  346  364  366  361                                       Mold relea-                                                                         1.5  1.5  1.5  1.5  1.5  1.5  1.5                                       sing agent                                                                    Coupling                                                                            2.0  2.0  2.0  2.0  2.0  2.0  2.0                                       agent                                                                         __________________________________________________________________________     Note 1:                                                                       glycidyl ether of ocresol novolak; SUMIEPOXY ® ESCN195 available from     SUMITOMO Chemical Co. Ltd. (Epoxy equivalent weight; 201 g/eq.,               Hydrolyzable chlorine content; 330 ppm)                                  

                                      TABLE 2                                     __________________________________________________________________________                              Comp.                                                                              Comp.                                                                              Comp.                                     Ex. 9      Ex. 10                                                                             Ex. 11                                                                             Ex. 12                                                                             Ex. 3                                                                              Ex. 4                                                                              Ex. 5                                     __________________________________________________________________________    Spiral                                                                              65   60   60   52   53   48   57                                        flow (in)                                                                     Barcol                                                                              61   75   71   80   78   50   0                                         hardness                                                                      (B)                                                                           Glass 145  166  163  152  168  130  110                                       transition                                                                    temp. (°C.)                                                            Flexural                                                                            14   14   13   13   13   14   14                                        strength                                                                      (kg/mm.sup.2)                                                                 Flexural                                                                            1460 1370 1350 1370 1350 1360 1420                                      modulus                                                                       (kg/mm.sup.2)                                                                 Water                                                                         absorbance                                                                    24 hrs.                                                                             0.13 0.15 0.15 0.14 0.25 0.20 0.15                                      72 hrs.                                                                             0.23 0.28 0.27 0.27 0.37 0.33 0.27                                      __________________________________________________________________________

What is claimed is:
 1. A process for encapsulating a semiconductor device which comprises encapsulating a semiconductor device with an epoxy resin composition comprising (a) an epoxy resin represented by the general formula (2) ##STR9## wherein R₁ to R₄ independently represent hydrogen, an alkyl or cycloalkyl group having 1 to 9 carbon atoms, or halogen, and X represents hydrogen, an alkyl group having 1 to 9 carbon atoms, or an aryl and n represents an average number of repeating units of 0.1 to 1.6; and a curing agent.
 2. A process according to claim 1, wherein said curing agent is present in an amount of 0.7 to 1.2 equivalents based on the epoxy group, X is selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, phenyl and naphthyl, and R₁, R₂, R₃, and R₄ are each independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, chlorine, and bromine.
 3. A process according to claim 1, wherein said curing agent is present in an amount of 0.7 to 1.2 equivalents based on the epoxy group.
 4. A process according to claim 3, wherein X is selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, phenyl and naphtyl.
 5. A process according to claim 3, wherein R₁, R₂, R₃, and R₄ are each independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, chlorine, and bromine.
 6. A process according to claim 1, wherein R₁, R₂, R₃, and R₄ are each independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, chlorine, and bromine.
 7. A process according to claim 6, wherein X is selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, phenyl and naphthyl.
 8. A process; according to claim 1, wherein X is selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, phenyl and naphthyl.
 9. An encapsulated semiconductor device obtained by encapsulating a semiconductor with an epoxy resin composition comprising (a) an epoxy resin represented by the general formula (2) ##STR10## wherein R₁ to R₄ independently represent hydrogen, an alkyl or cycloalkyl group having 1 to 9 carbon atoms, or halogen, and X represents hydrogen, an alkyl group having 1 to 9 carbon atoms, or an aryl and n represents an average number of repeating units of 0.1-1.6; and a curing agent.
 10. An encapsulated semiconductor device according to claim 9 wherein said epoxy resin composition further contains at least one additive selected from the group consisting of fillers, curing accelerators, flame retardants, mold releasing agents, and surface treating agents.
 11. An encapsulated semiconductor device according to claim 9 wherein said epoxy resin composition further contains a flame retardant.
 12. An encapsulated semiconductor device according to claim 9 wherein said epoxy resin composition further contains a filler.
 13. An encapsulated semiconductor device according to claim 9 wherein said epoxy resin composition further contains a mold releasing agent.
 14. An encapsulated semiconductor device according to claim 9 wherein said curing agent is present in the uncured epoxy resin composition in an amount of 0.7 to 1.2 equivalents based on the epoxy group.
 15. A process according to claim 1 wherein said epoxy resin composition further contains at least one additive selected from the group consisting of fillers, curing accelerators, flame retardants, mold releasing agents, and surface treating agents.
 16. A process according to claim 1 wherein said epoxy resin composition further contains a flame retardant.
 17. A process according to claim 1 wherein said epoxy resin composition further contains a filler.
 18. A process according to claim 1 wherein said epoxy resin composition further contains a mold releasing agent. 